Wayne,
You're correct that the drought situation in California (at least Northern
California) has improved since this past winter. Redding is currently
almost 10" above normal rainfall for the year, which is a pretty
significant turnaround. That said, the multi-year drought impacted a
significant amount of habitat out there, particularly in Southern
California and the Central Valley. My idea was that food sources may be
more scarce than usual in these areas and that migrants would spend less
time in these spots, effectively moving northward more quickly than usual.
Of course, native California vegetation tends to be *very*
drought-resistant, which is how it survived the decades-long "megadroughts"
several centuries ago.
(See here for more info:
http://news.nationalgeographic.com/news/2014/02/140214-drought-california-prehistory-science-climate-san-francisco-2/
)
On the other hand, human activity has destroyed much of this
climate-adapted vegetation and replaced it with crops, invasive grasses,
weeds, palm trees, etc. And much of that stuff got absolutely fried between
2013 and 2015. The lowering of the water table in the Central Valley has
also either killed or stressed native plants (particularly the Valley
Oaks), which makes the surviving plants even more susceptible to drought
stress. So even if there's water from this winter's rainfall, there might
not yet be enough vegetation in these areas to support the typical
population of insects, and this would give birds less of a reason to hang
around during migration.
Brandon
Eugene
On Fri, May 27, 2016 at 8:12 AM, <whoffman@xxxxxxxx> wrote:
Hi -
I agree with your statement about California, but iIthink this year it is
not as dry down there as last year.
It is important to remember that birds' decisions to migrate within a
given season presumably have to be based on conditions where they are,
rather than conditions where they are headed. As far as we know, they do
not have access to the Weather Channel.
Wayne
